**3. Conclusions**

different types of multifunctional VADS satisfying different vaccination requirements. As a proved by numerous experiments, at least in animal models, these multifunctional liposome VADSs are highly effective in both targeting delivery of vaccine to APCs and enhancing Ag presentation by APCs to related T-cells to set up the Ag-specific immunity against pathogens,

fulfilling a dual function of adjuvancy and delivery for vaccines [7, 37, 47–49].

18 Immunization - Vaccine Adjuvant Delivery System and Strategies

saponin were noticed thanks to its tight association with cholesterol.

product ISCOPREP™ saponin by omitting QH-A fraction [57].

CD8α+

**2.4. VADS constructed with ISCOMs formed by self-assembly of saponin and lipids**

The immune stimulating complexes, named ISCOMs, are a type cage-like NPs with a size of 40 nm constructed of linked nanoring subunits with a size of 12 nm, and usually formed through self-assembly of the main components of phospholipids, cholesterol and, importantly, saponin which, as a crude mixture of numerous triterpene derivatives extracted from the cortex of the South-American Tree *Quillaja saponaria Molina*, has potent adjuvant activities [52]. ISCOM was first coined the name in 1984 by Morein et al. [53], who demonstrated that ISCOMs contained saponin Quil A, a heterogeneous mixture containing up to 23 different saponin compounds [54], and virus membrane proteins were at least 10 times more potent than micelles formed by aggregation of the protein Ags alone, but caused no severe side effects, such as hemolysis, associated with saponin. The strong immunostimulatory effects were argued to be resulted from large exposure of protein Ags in ISCOMs and the intrinsic adjuvanticity of saponin Quil A, while no severe adverse effects of hemolysis associated with

Being explored for high potency and low toxicity, Quil A was purified using reversed phase high performance liquid chromatography (RP–HPLC), by which Kensil et al. identified adjuvant activity in 10 of the fractions including the four most abundant compounds, termed QS-7, 17, 18, and 21, with the numbers corresponding to their relative elution time, which is dependent on their degree of hydrophobicity using C4 resin column with RP–HPLC [55]. Similarly, Rönnberg et al. isolated three different RP–HPLC fractions of Quil A: QH-A sequences eluted early, further two sequences of the more hydrophobic fractions QH-B and QH-C, which were examined by pre-clinical toxicology and animal testing, resulting in an optimized combination of 7 parts QH-A, 0 parts QH-B and 3 parts QH-C, known as QH-703 or ISCOPREP™703 (Iscotec AB, Sweden) [56], which was further developed into proprietary

The identification of purified adjuvants from crude saponin allows ISCOMs to be formulated with more defined ingredients, such as monomer of QS21, ISCOPREP™ 703, and ISCOPREP™ [54], to constitute a VADS which can induce robust immunoresponses with Ags whether incorporated in the carrier or just physically mixed with the carrier [58, 59]. Formulation requiring no Ag incorporation not only simplifies the process of preparing the ISCOM vaccines but also expands the delivered Ags to include the hydrophilic ones; and the findings further supports the hypothesis that encapsulation of Ags in a carrier is not necessarily the prerequisite requirements for stimulating immunoresponses [60]. Duewell et al. developed the palmitified OVA-incorporated ISCOMs consisting of ISCOPREP, PC and cholesterol and showed that subcutaneous injection of OVA-ISCOMs to mice resulted in a substantial influx and activation of immune effector cells in dLNs in control of the vaccinated site and promoted natural killer (NK) and NK T cells to produce IFN-γ. Also, facilitated by the efficient Ag cross-presentation

DCs in dLNs, a high frequency of different tumor cell killing Ag-specific CTLs was

The NP-based VADSs provide an efficient strategy for delivering and enhancing efficacy of subunit vaccines, which are weak immunogens but represent the current trends in the development of vaccines against various pathogens including cancer. The NPs formed through self-assembly of small molecules, especially, those possessing intrinsic adjuvanticity, are an attractive and promising VADS due to their numerous advantages, such as acceptable safety profile, ease for preparation and modification with functional materials as well as control of size, and fitting different vaccination routes, which may confer the carried vaccines multiple functions capable of eliciting the Ag-specific humoral as well as cellular immunity at both systemic and mucosal levels providing a strong protection against pathogens. Encouragingly, some subunit vaccines developed with the VADSs that are based on small molecule-assembled NPs have already been approved for clinical vaccination, and typical products include the virosome-based hepatitis A vaccine (Epaxal®) and influenza vaccine (Inflexal V®), MF59 based influenza vaccine (Fluad®), AS04-based HPV (Cervarix®) and HBV (Fendrix®) vaccines, and AS01-based malaria vaccine (Mosquirix®). Hopefully, as many problems associated with NP VADSs, such as high cost for products, and undefined mechanisms underlying immune reactions and associated adverse effects, are finally settled, more NP VADS-based subunit vaccines will be pushed into markets for conquering human life-threatening diseases, such as HIV infection, MERS infection, and even intractable cancers.

**References**

441-450

**16**(12):1709-1719

[1] Plotkin SA. Vaccines: The fourth century. Clinical and Vaccine Immunology. 2009;

Vaccine Adjuvant Delivery Systems Constructed Using Biocompatible Nanoparticles Formed…

http://dx.doi.org/10.5772/intechopen.79905

21

[2] Germain RN. Vaccines and the future of human immunology. Immunity. 2010;**33**(4):

[3] Gregory AE, Titball R, Williamson D. Vaccine delivery using nanoparticles. Frontiers in

[4] Skwarczynski M, Toth I. Recent advances in peptide-based subunit nanovaccines.

[5] Coffman RL, Sher A, Seder RA. Vaccine adjuvants: Putting innate immunity to work.

[6] Wang X, Wang N, Li N, Zhen Y, Wang T. Multifunctional particle-constituted microneedle arrays as cutaneous or mucosal vaccine adjuvant-delivery systems. Human Vaccines

[7] Wang T, Zhen YY, Ma XY, Wei B, Wang N. Phospholipid bilayer-coated aluminum nanoparticles as an effective vaccine adjuvant-delivery system. ACS Applied Materials

[8] Wang T, Wang N. Preparation of the multifunctional liposome-containing microneedle arrays as an oral cavity mucosal vaccine adjuvant-delivery system. Methods in Molecular

[9] Wang T, Wang N. Biocompatible mater constructed microneedle arrays as a novel vaccine adjuvant-delivery system for cutaneous and mucosal vaccination. Current Phar-

[10] Wang N, Wang T. Preparation of multifunctional liposomes as a stable vaccine deliveryadjuvant system by procedure of emulsification-lyophilization. Methods in Molecular

[11] Di Pasquale A, Preiss S, Tavares Da Silva F, Garcon N. Vaccine adjuvants: From 1920 to

[12] Akira S. Innate immunity and adjuvants. Philosophical Transactions of the Royal Society

[13] Sahdev P, Ochyl LJ, Moon JJ. Biomaterials for nanoparticle vaccine delivery systems.

[14] McKee AS, Marrack P. Old and new adjuvants. Current Opinion in Immunology. 2017;

[15] Masson JD, Thibaudon M, Belec L, Crepeaux G. Calcium phosphate: A substitute for

Cellular and Infection Microbiology. 2013;**3**:1-13

& Immunotherapeutics. 2016;**12**(8):2075-2089

Immunity. 2010;**33**(4):492-503

& Interfaces. 2015;**7**(12):6391-6396

maceutical Design. 2015;**21**(36):5245-5255

2015 and beyond. Vaccines (Basel). 2015;**3**(2):320-343

Pharmaceutical Research. 2014;**31**(10):2563-2582

of London. Series B, Biological Sciences. 2011;**366**(1579):2748-2755

aluminum adjuvants? Expert Review of Vaccines. 2017;**16**(3):289-299

Biology. 2016;**1404**:651-667

Biology. 2016;**1404**:635-649

**47**:44-51

Nanomedicine (London, England). 2014;**9**(17):2657-2669
